This invention relates generally to a speed change gearing mechanism for motor vehicles and, more specifically, to such a mechanism for controlling both main and sub-speed change gears.
In prior art multiple stage speed change gear devices provided with both a main speed change gear and a sub-speed change gear, the gears of the main speed change gear and sub-speed change gear are respectively changed over by operating their separate and individual speed change levers. In this prior art device, a combination of gears of the main speed change gear and sub-speed change gear is selected by the two speed change levers and therefore a driver's judgement is required for a proper selection. Furthermore, it is rather cumbersome for a driver to operate the two speed change levers in a narrow driver's seat and occasionally during operation of one speed change lever the driver's hand may inadvertently touch the other speed change lever, resulting in undesired operation. Accordingly, the conventional devices pose a problem in that the time and care required for the speed change operation is greater than required by devices which use a single speed change lever.
On the other hand, there has been proposed a device in which changing over of gears of a sub-speed change gear is achieved by a fluid pressure actuator, and a fluid circuit of the fluid pressure actuator is operated by means of an electric switch mounted on an operating lever of a main speed change gear. In this device a driver may easily accomplish the speed change operation but is not always aware of the stage of speed change operation performed. This can result in a possible overrun of the engine or the like caused by improper speed change operation. In addition, operating mechanisms controlled by electrical means or fluid pressure must be provided and therefore the cost of manufacture is increased.
In order to solve these problems noted above with respect to prior art devices, it is an object of the present invention to provide a multiple stage speed change gear device in which both main and sub-speed change gears are operated by a single speed change lever.